Transmission control fail safe system

ABSTRACT

Electrohydraulic control for an automatically shiftable automotive transmission with a selection slide valve (2), at least for the neutral position (N), as well as for the drive mode (D) and reverse mode (R), an electronic control device (3) having solenoid valves (4) held in neutral position by spring action, a pressure-medium source (1), pressure control and gear control valves (5, 6, 7) for the actuation of gear engagement couplings and brakes (A-F), as well as with a R-gear safety valve (8), for preventing the shifting into the R-gear when the forward drive speed is still too high, and a system which, in the case of electronic failure, holds or shifts the automatic transmission to one gear insuring that the maximum permissible rotational speed of the engine is not exceeded when the vehicle travels at maximum speed, whereby, in the event of failure of the electronic control device (3) during driving, a control system holds or shifts the gear, and in the event of failure of the electronic control device (3) before the start or the restart of the engine, this control system (5, 6, 7, 8, 9) engages a lower gear. This way, in the case of electronic failure during travel, travel can be continued unhampered, for instance also in the highest gear, and no shifting down takes place. When the electronic device fails at start or at restart after a failure during travel, a lower gear is engaged, wherein it is also possible to start the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application corresponding toPCT/EP87/00423 filed Aug. 1, 1987 and based in turn upon an applicationfiled in Luxembourg as PCT/EP86/00469 filed Aug. 8, 1986 under theInternational convention.

FIELD OF THE INVENTION

My present invention relates to an electrohydraulic control for anautomatically shiftable automotive transmission. More particularly, theinvention relates to an electrohydraulic control for an automaticallyshiftable automotive transmission with a selection slide valve at leastfor the neutral position as well a for the drive mode and the reversemode, an electronic control device, solenoid valves held in the neutralposition by spring action, a pressure-medium source, pressure controlvalves and gear shift control valves for actuating the gear engagementclutches and brakes, a reverse-gear safety valve which prevents theshifting into the reverse gear when the forward drive speed is too highand a system which, in the event of failure in the electronic circuitry,holds or shifts the automatic transmission into a gear insuring that themaximum permissible rotational speed of the engine is not exceeded whenthe vehicle travels at maximum speed.

BACKGROUND OF THE INVENTION

A 4-speed automatic transmission with electronic-hydraulic control isknown from two publications in ATZ 85 (1983), 6 pages 393 to 405. Fromparagraph 4, Transmission Control (page 402) and paragraph 5, SafetyFunctions, as well as from FIGS. 6 and 7 of these prior artpublications, it is known that in a currentless state, the vehicle canbe driven purely hydraulically, corresponding to the selection slidevalve shift, either forward in the 3rd speed or in reverse, whereby aneutral position (idling setting) is also possible.

In the publication 4 HP 22 E of the ZF GETRIEBE GMBH SAARBRUCKEN, OilCircuit Diagrams, this electronic-hydraulic transmission is illustratedin detail and completes FIG. 6. This system is possible because itcontrols an overdrive transmission, wherein the 4th speed is ahigh-speed gear--overdrive- and the engine does not reach the highestrotational speed. However, such a control is not appropriate for a4-speed transmission with a direct 4th speed or an overdrivetransmission wherein the highest rotational speed is reached in thehighest gear, because a shifting down from the 4th to the 3rd speed incase of electric-current supply failure leads to excessively highrotational speeds in the engine and could result in damage to theengine.

OBJECTS OF THE INVENTION

It is, therefore, an object of the present invention to provide animproved electronic-hydraulic control of the type described, so that incase of electric-current supply failure no unacceptable downshiftingoccurs.

It is also an object to achieve this result without an increase in thecost of construction.

SUMMARY OF THE INVENTION

This object is attained providing the electronic device so that the gearin which the maximum permissible rotational speed is not exceeded isheld only during travel by a control system or the transmission isshifted into this gear, and during failure of the electronic controldevice, this system engages a lower gear before starting or restartingof the engine.

During operation at high speed, the driver does not become aware of afailure in the electronic control from the behavior of the vehicle,until the provided signal appears on the dashboard, and under suchconditions he can continue to drive unimpaired. Also, the engine is notoverloaded, since no inadmissible shifting down, which could lead toengine damage, takes place. Only when certain requirements can no longerbe met in this speed, e.g. driving uphill, will the driver have thepossibility to shift the transmission into a lower gear. However, forthis purpose the system pressure has to be interrupted for a short whilefor the hydraulic part of the electronic-hydraulic control to respond.For safety reasons, the driver has to stop the engine for this purposeand then restart it. Of course, it would also be possible to carryout-this shifting to a lower gear by shifting the selection slide valveinto the neutral position and again back into drive. But, such a controlsystem will not meet safety requirements, since the driver would havethe possibility to shift when the driving speed is still too high.According to the invention, independently of the failure of theelectronic control device, after the start or restart of the engine andthe shifting of the selection slide valve into the reverse mode, is itpossible to drive in reverse. Alternatively, independently of thefailure of the electronic control device, when the selection slide valveis shifted into the R-mode, it is possible to drive in reverse.

Moreover, with a failed electronic control device after the start of theengine and by shifting the selection slide valve into the drive mode, astart in a predetermined lower drive gear is possible.

The control system is advantageously a hydraulic control system for a4-speed automatic transmission with three gear control valves, a R-gearsafety valve and a further control valve. As a control valve a safetyvalve is provided, and that the hydraulic control system consists ofthis safety valve and the available three-gear control valves, as wellas of the reverse-gear safety valve. A pressure medium source isconnected via a conduit which the main pressure valve, the selectionslide valve and a channel for the system pressure. The selection slidevalve is connected via a channel for the system pressure with thecoupling for the forward drive and a fifth annular space of the 1-2 gearcontrol valve and via a channel, which is filled with system pressurewhen the selection slide valve is shifted into R-gear, with a secondannular space of the R-gear safety valve.

A system-pressure branch of channel leads to the pressure-reducingvalve, as well as to a third annular space of the safety valve and to afifth annular space of the 3-4 gear control valve. A reduced pressure isdirected as control pressure via a control-pressure line to the solenoidvalves and these are connected via an electric control line with theelectronic control device.

From the first solenoid valve a first control line leads to a secondannular space of the 3-4 gear control valve and to a spring space of the1-2 gear control valve, and from the second solenoid valve a secondcontrol line leads to the first frontal annular spaces of the R-gearsafety valve, the 1-2- and 2-3- gear control valves and of the safetyvalve, as well as to a fifth annular space of this safety valve.

All gear control valves and the R-gear safety valve and the safety valvehave annular spaces, formed in their housings and a spool valve eachkept in an end position by the pressure of a respective compressionspring located in the respective spring spaces.

The 1-2 gear control valve has another pressure-medium connection fromthe third annular space via a duct and a second ball valve to thereverse-gear brake, and the sixth annular space is connected via theconduits to the fifth annular space of the 2-3 gear control valve andthe second and seventh annular space have a vent. The spool valve hasthree control pistons for the formation of the control edges.

The 2-3 gear control valve has another pressure-medium connection fromthe third annular space via conduit to the brake and from the sixthannular space via a conduit, the first ball valve and a further conduitto a clutch, and over the fourth annular space via a conduit to a brake.The second and the seventh annular spaces have a vent. The spool valvehas three control pistons for the formation of control edges.

The 3-4 gear control valve has another pressure-medium connection fromthe fourth annular space over a conduit to a further brake for the 1stto 3rd speeds and the R-gear and from the sixth annular space throughthe conduit to the clutch for the 4th speed. The third and seventhannular spaces have vents. The respective spool valve has four controlpistons for the formation of control edges. The R-gear safety valve hasanother pressure-medium connection from the third annular space via aduct and a second ball valve to the R-gear brake and over a conduit andthe first ball valve and a conduit to the respective clutch, and fromthe conduit an additional branch leads to the spring space of the safetyvalve. The fourth annular space has a vent and its spool valve has twopistons for the formation of control edges.

The safety valve is another pressure-medium connection from the fourthannular space over a conduit to the first frontal annular space of the3-4 gear control valve. The second annular space has a vent and therespective spool valve has three control pistons for the formation ofcontrol edges. There is yet another pressure-medium connection from therespective conduits through a third, only unilaterally opening ballvalve to the channel and thereby to the first clutch.

In the event of failure of the electronic control device during drivingand the associated venting of its control lines via the system pressurechannel, the safety valve is kept in its connected position and throughthe 3-4 gear control valve the clutch for the 4th speed is closed. Viathe system-pressure channel the first clutch is directly closed and viathe 1-2 gear control valve, the respective brake is closed and via theconduits, the 2-3 gear control valve and the first ball valve, thesecond clutch is closed.

Alternatively, in the event of failure of the electronic control deviceprior to starting or restarting the engine and the actuation of theselection slide valve in forward drive, the system pressure is directedto a channel through the safety valve and to the 3-4 gear control valveand displaces the same against the pressure of a spring, whereby theclutch for the 4th speed is vented and its brake is closed through thesystem pressure from the channel. Via the system-pressure channel, thefirst clutch is directly closed and via the 1-2 gear control valve andthe respective conduits, the respective brake is closed. Via the 2-3gear control valve and the first ball valve, the second clutch isclosed.

A shifting of the selection slide valve in the position for the reversemode (R), however, results in travel in this direction, although a lowergear has been selected in the drive mode range.

With the shifting of the automatic transmission into a lower gear, e.g.the 3rd speed, in a 4-speed transmission, in the case of start orrestart when the electronic control has failed, it is also possible tostart in the forward direction from the stationary position. By usingthe shift valves and control valves, which are anyway required for thehydraulic control effectuating the continuous drive and the start inforward driving and reverse driving directions in case of electronicfailure without damage to the engine, the cost of construction is notincreased. Solely through the unique connection of the two safety valveswith the three gear control valves, this problem is solved in anelectronic-hydraulic control for a 4-speed automatic transmission. Dueto the multiple use of a solenoid valve, it is possible to avoid theneed for an additional solenoid valve for the R-speed safety.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a diagram of a 4-speed automatic transmission with a direct4th speed;

FIG. 2 is a diagram of a 4-speed automatic transmission according toFIG. 1, but with an overdrive;

FIG. 3 is a table of the activation of the clutches, brakes and solenoidvalves in the individual speeds in a transmission according to FIG. 1;

FIG. 4 is a simplified control and oil-circuit diagram; and

FIG. 5 is a simplified control and oil-circuit diagram of a furtherembodiment.

SPECIFIC DESCRIPTION

The automatic transmission G1 according to FIG. 1 is driven by a drivingengine (not shown) via hydrodynamic torque converter W with by-passclutches UK and consists of a basic transmission G with the clutches Aand B, as well as the brakes C', C and D and an auxiliary transmissionGR 1 for the 4th speed with the clutches E and the brake F. Further, forthe improvement of the shifting and control, unmarked freewheeling unitsare arranged in the basic transmission as well as in the auxiliarytransmission.

In the automatic transmission according to FIG. 2, the arrangement ofthe hydrodynamic torque converter W and of the basic transmission G isthe same as in FIG. 1, only the auxiliary transmission GR 2 is connectedin a different way with the basic transmission G, and the clutch E andbrake F are differently arranged.

From the Table according to FIG. 3, where dots represent actuatedstates, which applies to transmission G1 in FIG. 1, it can be easilyunderstood which clutches and brakes A to F and solenoid valves 4a and4b are closed in the individual speeds and are connected anddisconnected by the electronic-hydraulic control, and in the case of thesolenoid valves by the electronic control device 3, and with referenceto the clutches and brakes, actuated with system pressure.

In the simplified control diagram according to FIG. 4, a pressure-mediumsource 1 is connected via a conduit 10 with a main pressure valve 11, aswell as with a selection slide valve 2 and the system-pressure channel13. The selection slide valve 2 has another connection via channel 21with the clutch A for the forward drive mode, as well as with the 5thannular space 55 of the 1-2 gear control valve 5.

Furthermore, from the selection slide valve 2, another channel 22 leadsto the second annular space 82 of the reverse speed safety valve 8,which however is actuated by system pressure only when the selectionslide valve is shifted into the reverse mode (R).

The system-pressure channel 13 has a branch leading to thepressure-reducing valve 12, as well as to the third annular space 93 ofthe safety valve 9 and to the fifth annular space 75 of the 3-4-gearcontrol valve 7.

From the pressure-reducing valve 12, via the control-pressure line 43,the solenoid valves 4a and 4b are supplied with control pressure.

The solenoid valves 4a and 4b are switched by the electronic controldevice 3 via the electric control line 31 and are vented whendisconnected.

From the first solenoid valve 4a, a first control line 41 leads to thesecond annular space 72 of the 3-4-gear control valve 7 and to thespring space 58 of the 1-2 gear control valve 5.

The second control line 42 leads from the second solenoid valve 4b tothe first frontal annular spaces 51, 61, 81, 91 of the gear controlvalves 5, 6 and of the reverse-speed safety valve 8 and of the safetyvalve 9, as well as to the fifth annular space 95 of this safety valve9.

All gear control valves 5, 6, 7, the reverse-speed safety valve 8 andthe safety valve 9 have several annular spaces 51-57, 61-67, 71-77,81-84, 91-95 worked into the housing and for each a spool valve slider50, 60, 70, 80, 90 is provided, each being pushed into an end positionby a compression spring 59, 69, 79, 86 and 97, respectively, arranged inthe spring spaces 58, 68, 78, 85, 96.

The 1-2-gear control valve 5 has also a pressure-medium connection fromthe third annular space 53 via the duct 530 and the second ball valve K2to the reverse-speed brake D.

The sixth annular space 56 is connected via duct 560, 561 with the fifthannular space 65 of the 2-3-gear control valve 6, and the second annularspace 52 and the seventh annular space 57 have a vent, while the spoolvalve slider 50 has three control pistons 501, 502 and 503, formingcontrol edges.

The 2-3-gear control valve 6 has also another pressure-medium connectionfrom the third annular space 63 via the duct 630 to the brake C' andfrom the sixth annular space 66 via the duct 660, the first ball valveK1 and the duct 661 to the clutch B. Further, a duct 640 leads from thefourth annular space 64 to the brake C and the second and seventhannular spaces 62, 67 have a vent. The spool valve slider 60 has threecontrol pistons 601, 602 and 603 for the formation of control edges.

The 3-4 gear control valve 7 has also a pressure-medium connection fromthe fourth annular space 74 via the conduit 740 to the brake F for thespeeds 1 to 3 and the R-speed, and from the sixth annular space 76 viathe conduit 760 to the clutch E for the 4th speed. The third and seventhannular spaces 73 and 77 have a vent and the spool valve slider 70 hasfour control pistons 701-704 for the formation of control edges, wherebythe control piston 701 has a smaller diameter in comparison to theremaining control pistons.

The reverse-speed safety valve 8 has also an additional pressure-mediumconnection from the third annular space 83 via the conduit 830 and thesecond ball valve K2 to the reverse-speed brake D and via the conduit831 and the first ball valve K1 and the conduit 661 to the clutch B. Abranch 832 of the conduit 830 leads to the spring space 96 of the safetyvalve 9, and the fourth annular space 84 has a vent. The spool valveslider 80 has two control pistons 801 and 802 for the formation ofcontrol edges.

The safety valve 9 has another pressure-medium connection from thefourth annular space 94 via the conduit 940 to the first frontal annularspace 71 of the 3-4 gear control valve 7, and the second annular space92 has a vent. The spool valve slider 90 has also three control pistons901-903 for forming control edges, whereby the control piston 901 has asmaller diameter than the remaining control pistons 902 and 903.

Further, there is a connection conduit 562, 564 from the conduit 560 tothe conduit 640 and to the channel 21, and thereby to the clutch A.Between the connection conduit 564 and the channel 21, extra supply lineto clutch A, there is a third ball valve K3, which allows onlyunidirectional flow passage in the described direction.

The electronic-hydraulic control device according to FIG. 4 works asfollows: The electronic control device 3 is connected to the solenoidvalves 4a and 4b. Further, the electronic device takes over theadjustment of the modulation pressure and the engagement of theconverter-bypass clutch; both are not shown in the simplified controldiagram according to FIG. 4.

When the electrohydraulic control is fully functioning, in the firstspeed, the solenoid valve 4b is engaged by the electronic control device3, so that over the second control line 42 the gear control valves 5, 6and 7 are shifted against the pressure of the springs 59, 69 and 79.

Over the channel 21 the coupling A is closed and over the channel 13 andthe conduit 740 the brake F is closed. According to FIG. 3, in the 2ndspeed the solenoid valve 4a is also engaged, so that via the firstpressure line 41 control pressure is supplied to the spring space 58 ofthe 1-2-gear control valve 5 and the second annular space 72 of the3-4-gear control valve 7. The 1-2-gear control valve 5 is thereby pushedback into its initial position. As a result, the system pressure fromchannel 21 can close the brake C via the annular spaces 55 and 56 andthe conduits 560, 562 and 563, and can close the brake C' via theconduit 640 and the annular spaces 64 and 63 of the 2-3-gear controlvalve 6 as well as the conduit 630.

In the 3rd speed the solenoid valve 4b is disconnected and the secondcontrol line 42 is vented via the solenoid valve. As a result, the2-3-gear control valve 6 goes back to its initial position, and thebrake C' is vented over the conduit 630 and the annular spaces 62 and63. At the same time, via the conduit 561 and the annular spaces 65 and66 of the 2-3-gear control valve 6 via the conduit 660, the first ballvalve K1 and the conduit 660 the coupling B is closed.

In the 4th speed, the solenoid valve 4a is also disconnected and thefirst control line 41 is vented. Thereby, the 3-4-gear control valve 7goes back to its initial position, the brake F is vented via the conduit740 and the fourth and third annular space and the clutch E is closedvia the channel 13, the fifth and sixth annular space and the conduit760. This combination makes it possible to connect without delay thegear control valves 5, 6 and 7, as desired. Also, with the solenoidvalve 4b the R-gear safety valve 8 can be actuated at the same time. Inthis way, it is possible to save one solenoid valve.

The gear control valves 5, 6 and 7 are hydraulically locked against eachother, so that no erroneous shifting, leading to the blocking ordestruction of the transmission, can occur.

At the electronic recognition of the selection of position R by theselection slide valve 3 and at a limit speed, additionally to thesolenoid valve 4a, also the solenoid valve 4b is connected. Via thesecond control line 42 the reverse-gear safety valve 8 is pushed via theannular space 81 against the force of the spring 86 and thereby thesystem pressure coming from the select ion slide valve 3 via the channel22 is blocked in the second annular space. Only when the speed hasdecreased below the limit speed or threshold is the solenoid valveelectronically disconnected and via the annular space 82 and 83 and theconduit 830 and the second ball valve K2 the reverse-mode brake D can beclosed, while via the conduit 831 and the first ball valve K1, as wellas the conduit 661, the clutch B can be closed.

In case of failure of the electronic control device 3 during travel andtherewith connected venting of the control lines 41 and 42, the safetyvalve is maintained in the connected position in the annular space 93 bythe system pressure from channel 13.

The 3-4-gear control valve is in the end position determined by thespring 79, so that system pressure from the channel 13 passes via theannular spaces 75 and 76 and the conduit 760 to the clutch E and closessame. Via the system-pressure channel 21 the clutch A is directlyclosed, and via the 1-2-gear control valve, the annular spaces 55 and56, as well as the conduits 560, 562 and 563 the brake C is closed. Viathe conduit 560, 561 and the 2-3-gear control valve 6, annular spaces 65and 66, as well as the conduit 660 and the first ball valve K1 and theconduit 661 the coupling B is also closed. Thereby, the 4th speed isheld or connected and it is possible to travel at this time only in thisspeed. In order to continue travelling in a lower speed or in order tostart the vehicle, it is necessary first to interrupt the systempressure for a short time. For this purpose, the engine has to be turnedoff and then to be restarted again, since this insures that when thetransmission is shifted into a lower gear, in which it is also possibleto start, the rotational speed of the engine is not inadmissibly high.

When the engine is started anew, the system pressure comes via thechannel 13, the annular spaces 93, 94 and the conduit 940 to the annularspace 71. As a result, the 3-4-gear control valve 7 is brought into theillustrated position. When the selection slide valve is shifted from theposition N (neutral), where it was started, to the position drive, thesystem pressure from channel 13 is guided via the annular spaces 75 and74 and the conduit 740 to the brake F and this is closed, while thecoupling E is vented via the conduit 760 and the annular spaces 76 and77. Via the channel 21, the coupling A is directly closed by the systempressure and via the 1-2-gear control valve 5 and the conduits 560, 561,563 the brake C is closed, via the conduit 560, 561, the 2-3-gearcontrol valve 6, the conduit 660, ball valve K1 and the conduit 661 thecoupling B is closed.

If the electronic control device 3 has failed and the selection slidevalve 2 is shifted into the R-gear, the system pressure reaches viachannel 22 the reverse-gear safety valve 8. Via the annular spaces 82and 83 the conduit 830 is thereby filled and over the second ball valveK2 the reverse gear brake D is closed and over the first ball valve K1and the conduit 661, the clutch B is closed.

At the same time, over the branch 832 of the channel 830, the systempressure is directed to the spring space 96 of the safety valve 9.Thereby, the system pressure from the channel 13 is directed via thethird and fourth annular spaces 93 and 94 and the conduit 940 to thefrontal first annular space 71 of the 3-4-gear control valve 7, so thatover the annular spaces 75 and 74 the system pressure from the secondbranch of the channel 13 over the conduit 740, the brake F is closed. Inthis shifting position of the 3-4-gear control valve the clutch E isvented.

FIG. 5 is a further embodiment of the invention and is very similar toFIG. 4. Differently from FIG. 4, however, in FIG. 5 the second controlline 42 does not lead to the frontal annular space 81 from the R-gearsafety valve 8, and the branch 832 from the conduit 830 to the springspace 96 is also not executed. Therefore, the conduit 940 leads not onlyto the first frontal annular 71 of the 3-4-gear control valve 7, butfurther as conduit 940a to the first frontal annular space 81 of theR-gear safety valve 8, and via channel 22a, the fourth annular space 84is connected therewith for the system pressure in the R-gear position ofthe selection slide valve 2, while the second annular space 82 isvented. With this variant of the channel- and conduit layout, thevehicle can be driven in reverse in the case of electronic failure,without having to interrupt the system pressure for a short time.

I claim:
 1. An automatically shiftable transmission for a vehicleincluding a gear mechanism and having a plurality of clutches and ofbrakes effective to switch the gear mechanism into a respective forwardand rear speeds, and an electrohydraulic control system, saidelectrohydraulic control system comprising:a pressure medium sourcesupplying a system pressure to said electrohydraulic system; a selectionslide valve receiving said system pressure from said pressure mediumsource for selecting between at least a forward drive mode including afirst, second, third and forth forward speeds, a neutral mode and areverse drive mode; a first solenoid valve and a second solenoid valveoperatively connected with said pressure medium source and supplying acontrol pressure to control shifting between said speeds, said solenoidvalves having a switched off position and a switched on positioncorresponding to said modes selected by said selection valve; anelectronic control device for controlling said first and second solenoidvalves: a first, second and third pressure-control and gear-shiftcontrol valves for actuating the gear engagement clutches and brakesreceiving said control and pressure system upon reaching the respectivefirst, second, third and forth speeds of the transmission; a reversegear-shift safety valve for preventing shifting of the transmission intosaid reverse mode upon an output speed of the transmission exceeding agiven forward output speed, said reverse-gear safety valve beinghydraulically interconnected with said pressure-control and with saidsolenoid valves and receiving said system and control pressures; and asafety valve hydraulically interconnected with said pressure-control andreverse-gear valves and receiving said control and pressure systems,said reverse-gear, pressure-control and safety valves constituting acontrolling system for holding the transmission in a respective gearupon not exceeding of the maximum permissible rotational speed or forshifting said transmission into said gear upon failure of saidelectronic device, said controlling system shifting said transmissioninto a lower gear upon starting of the engine.
 2. The automaticallyshiftable transmission defined in claim 1, further comprising:a mainpressure-medium valve receiving said system pressure from said source; apressure-reducing valve receiving said system pressure from saidmain-pressure valve and from said source and supplying said first andsecond solenoid valves with said control pressure; said firstsafety-control valve being a 1-2 gear selection valve formed with aspring space, a first annular space spaced from said spring space andwith a second, third, forth, fifth and sixth annular spaces between saidfirst and spring spaces; said second safety-control valve being a 2-3gear selection valve formed with a respective first annular space spacedfrom a respective spring space and with a respective second, third,forth, fifth and sixth annular spaces between said first and springspaces of said 2-3 gear selection valve; said third safety-control valvebeing a 3-4 gear-selection valve formed with a respective first annularspace spaced from a spring annular space and with a respective second,third, fourth, fifth and sixth annular spaces between said first andspring spaces of said 3-4 gear control valve: said reverse gear safetyvalve is formed with a respective first annular space and a respectivespring space spaced from one another and with a respective second, thirdand forth annular spaces located between said first and spring spaces ofthe reverse gear valve; said safety valve being formed with a respectivefirst and spring annular spaces spaced from one another and with arespective second, third, forth and fifth annular spaces between saidfirst and spring spaces of said safety valve; said pressure-mediumsource being connected with said main pressure valve through a firstconduit and with said manual selection valve via a second conduit, saidpressure source being connected with a system-pressure channel connectedwith said second conduit and with said pressure reducing valve; saidselection slide valve being connected with a first clutch for the drivemodes through a second conduit, said first clutch being connected withthe fifth annular space of said 1-2 gear control space through a forthconduit and with a first brake by a fifth conduit, said selection slidevalve being connected with the second annular space of said reversevalve through a sixth conduit, said reverse valve being actuated uponselecting said reverse move by said system pressure, the third annularspace of said safety valve being in communication with saidsystem-pressure channel through a seventh conduit and the fifth annularspace of said 3-4 gear valve being connected with said system-pressurechannel through an eighth conduit; said first and second solenoid valvesbeing connected with pressure-reducing valve through respective ninthand tenth conduits, said ninth conduit being connected with an eleventhconduit connecting said first solenoid valve with the second annularspace of said 3-4 gear control valve and with a twelfth conduit leadingto the spring space of said of 1-2 gear valve, said tenth conduit beingconnected with thirteenth, fourteenth, fifteenth and sixteenth conduitsleading respectively to the first annular spaces of said 1-2, throughsaid safety valve, via 2-3 and reverse valves and with a seventeenthconduit leading to the fourth annular space of the safety valve; thethird annular space of said 1-2 gear valve being connected with areverse-speed brake by an eighteenth conduit, the sixth annular space ofsaid 1-2 gear valve being connected with the fifth annular space of 2-3gear valve through a nineteenth conduit, the second and seventh annularspaces of said 1-2 gear valve being provided with respective vents; thethird annular space of said 2-3 valve having a connection with a secondbrake through a twentieth conduit; a second clutch being connectedthrough a twenty first conduit with a first ball valve therein with thesixth annular space of said 2-3 gear valve, a twenty second conduitleading from the fourth annular space of said 2-3 valve to said firstbrake: the third annular space of said 3-4 valve being connected with athird brake for said first, second, third and reverse speeds through atwenty third conduit, a twenty fourth conduit leading from the sixthannular space of said 3-4 valve to a third clutch for the fourth speed;the third annular space of said reverse valve being connected with saidreverse-speed brake through a twenty sixth conduit and through a secondball valve, said reverse-speed brake being connected with said secondclutch through a twenty seventh conduit, said third annular space of thereverse valve being connected with the spring space of said safety valvevia a thirty first conduit; the fourth annular space of said safetyvalve being connected with the first annular space of 3-4 valve througha twenty eighth conduit; the fourth space of said 2-3 valve beingconnected with said nineteenth conduit through thirtieth conduit andwith said selection valve and said first clutch by said third conduit,said third conduit being provided with a one way third ball valve. 3.The automatically shiftable transmission defined in claim 2 wherein saidsafety valve is provided with three axially movable control pistons andhaving a spring located in said spring space, said safety valve havingan engaged position upon moving said pistons toward said spring space,so that said spring is compressed, said safety valve being held in saidengaged position upon failure of said solenoid valves by receiving saidsystem pressure in the third annular space of said safety valve throughsaid system pressure channel and the seventh conduit, said third clutchfor the fourth speed being closed by said system pressure through saidtwenty fourth conduit of said 3-4 valve, said first clutch being closedupon the system pressure through said third conduit, said first brakebeing closed by said system pressure supplied through 1-2 valve,nineteenth, twenty ninth and via fifth conduits, said second clutchbeing engaged upon said system pressure through said 1-2 valve,nineteenth conduit, 2-3 valve and twenty first conduit, so that saidfourth speed is hold.
 4. The automatically shiftable transmissiondefined in claim 2 wherein said system pressure is directed to said 3-4valve through said pressure system channel, safety valve and twentyfifth conduit for displacing pistons provided in said 3-4 valve againsta pressure of a respective spring provided in the spring space of said3-4 valve, so that said system pressure coming through said systempressure channel closes said third brake upon venting said third clutchand closes said first clutch through said third conduit and said firstbrake through said nineteenth, twenty ninth and fifth conduits, saidsecond clutch being closed through said nineteenth conduit, 2-3 valveand through twenty first conduit and through said second ball valve, sothat said first forward speed is turned on upon failure of said solenoidvalves prior to starting the engine and the actuation of said selectionvalve in said forward mode.
 5. The automatically shiftable transmissiondefined in claim 2 wherein said system pressure is supplied through saidsixth conduit, said reverse valve and through said twenty fifth conduitand via said second ball valve to said rear brake, so that said rearbrake is closed, said system pressure supplying through said twentyseventh conduit and via said first ball valve to said second clutchthereby closing said second clutch, said brake for the fourth speedbeing closed by said system pressure coming through said third annularspace of said rear valve via said thirty first conduit to the springspace of said safety valve, said pistons of the safety valve beingpushed towards the respective first space, so that said system pressurefrom said system pressure channel through said twenty eighth conduit isled to said second annular space of said 3-4 valve closing said thirdbrake and venting said third clutch thereby driving the vehicle inreverse regardless of failure of said solenoid valves and upon shiftingsaid selection valve in said reverse mode.
 6. An automatically shiftabletransmission for a vehicle including a gear mechanism and having aplurality of clutches effective to switch the gear mechanism into arespective forward and rear speeds, and an electrohydraulic controlsystem, said electrohydraulic system comprising:a pressure medium sourcesupplying a system pressure to said system; a manual valve receivingsaid system pressure from said source and selecting a forward drive modeincluding at least a first speed, a second speed, a third speed and afourth speed, a neutral mode and a reverse mode; electronic meansconnected with said manual valve for determining the respective outputspeed of the transmission and including a first and second solenoidvalves, said solenoid valves supplying a control pressure to controlshifting between said speeds, said first solenoid valve being switchedon in said first speed of said manual valve; a plurality of hydraulicswitch valves receiving said system and control pressures forcontrolling actuation the respective clutches upon reaching therespective forward speed of the transmission; a reverse-gear valvereceiving said system and control pressures and hydraulically connectedwith one of said switch valves actuating the respective clutch upon saidfirst forward speed, said reverse-gear valve preventing the shifting ofthe gear mechanism into said reverse mode upon the output speed of thetransmission exceeding a given speed; and a safety valve hydraulicallyinterconnected with said switch and reverse-gear valves., said safetyvalve maintaining the fourth speed upon discontinuing of the controlpressure supply, said safety valve, said reverse and switch valveshydraulically controlling the subsequent actuation of said clutches inresponse to the change of said system pressure upon failure of saidelectronic means and upon a start of an engine.
 7. The automaticallyshiftable transmission defined in claim 6 wherein said control systemprovides said reverse mode upon the failure of said electronic means. 8.The automatically shiftable transmission defined in claim 6 wherein saidcontrol system provides an engine with a start at said first speed bycontrolling the engagement of the respective clutch.
 9. Theautomatically shiftable transmission defined in claim 6 wherein saidswitch, reverse and safety valves constitute a hydraulic control system.10. The automatically shiftable transmission defined in claim 6 whereinsaid plurality of the switch valves are;a 1-2 gear-selection valveformed with a respective first, second, third, fourth, fifth, sixth andspring annular spaces, a 2-3 gear selection valve formed with arespective first, second, third, fourth, fifth, sixth and spring annularspaces, a 3-4 gear selection valve being formed with a first, second,third, fourth, fifth, sixth and spring annular spaces, each of said gearselection, reverse and safety valves being formed with a respectivespring braced against a respective slide valve provided with a pluralityof pistons, the respective slide being axially movable in each of saidvalves, the fourth space of said 1-2 valve being connected with thefirst clutch through system pressure lines upon shifting said manualvalve in said forward drive mode and, the second annular space of said1-2 valve being connected through the pressure lines with said reversevalve upon shifting said manual valve to said reverse mode; said manualvalve being connected by an input pressure line with said source, saidinput pressure line being operatively connected with the third annularspace of said safety valve and with the fifth annular space of said 3-4gear selection valve, the second annular space of said 3-4 gearselection valve receiving said control pressure from the first solenoidvalve, a respective spring space of said 1-2 gear selection valvereceiving said control pressure through a first control line; saidsecond solenoid valve supplying the first annular space of said valvesspaced axially from the respective spring space and the fifth space ofsaid safety valve with said control pressure through a second controlline, the third annular space of said 1-2 gear control valve beingconnected to a reverse brake through said system pressure lines, thesixth annular space of the 1-2 gear valve being connected to the fifthannular space of the 2-3 gear valve by said system pressure lines; said2-3 gear control valve being connected with a second brake by its thirdannular space via said pressure system lines and by the sixth annularspace thereof with the second clutch, the fourth annular space of said2-3 gear valve being connected with a first brake; the fourth annularspace of said 3-4 gear valve being connected with a third brake by saidpressure system lines and with a respective gear, the sixth annularspace of the 3-4 gear valve being connected with the respective clutchfor the fourth speed, the slide valve of said 3-4 valve being providedwith four pistons, said reverse valve being connected with said secondclutch and with said reverse-gear brake through the system pressurelines, the spring space of said safety valve being connected with thethird annular space of said reverse valve, the respective slide valve ofsaid reverse valve being formed with two pistons, the fourth annularspace of said safety valve being connected with a first annular space ofsaid 3-4 valve spaced from the respective spring space of the 3-4 valveby the system pressure lines, the fourth annular space of the 2-3 gearvalve being connected with the first clutch by system pressure linesthrough a first unilaterally opening ball valve.
 11. The automaticallyshiftable transmission defined in claim 10, further comprises a secondball valve connected with said second clutch and a third ball valveconnected with said reverse-gear brake.
 12. The automatically shiftabletransmission defined in claim 10 wherein said safety valve operativelyconnected with the respective clutch for the fourth speed and with thesaid first and second clutches thereby keeping said clutches engaged andmaintaining the fourth speed upon failure of the solenoid valvessupplying the control system with the control pressure.
 13. Theautomatically shiftable transmission defined in claim 10 wherein saidsystem pressure being conveyed by said input pressure line through saidsafety valve to the 3-4 gear control valve upon selecting the drive modeby said manual valve and upon starting the engine, the respective slidevalve of said 3-4 gear valve being displaced so, that a brakecontrolling the fourth speed is engaged and the clutch for the fourthspeed is vented, the first clutch being engaged through said manualvalve and the second clutch being engaged through the 2-3 gear controlvalve, so that said transmission is able to be shifted gradually fromthe first speed to the fourth speed upon the failure of the solenoidvalves.
 14. The automatically shiftable transmission defined in claim 10wherein said system pressure is conveyed through said reverse valve tothe reverse-gear brake upon shifting said manual valve in the reversemode, so that said reverse-gear brake is engaged, said pressure systembeing led through said safety valve to said third brake thereby ventingsaid clutch for the fourth speed, so that the reverse mode is controlledupon the failure of the solenoid valves.